We are aware not all freshwater tropical fish are comfortable in waters with a strong current and that some fish are better served in water with minimal amount of movement (current). This knowledge suggests in home aquariums currents and water circulation should be considered an important aspect when choosing fish stocking, aqua-scaping and especially in the conception phase of aquarium set up and its implementation.

Current and water circulation are vital elements in aquatic ecosystems and is directly responsible for several necessary processes for maintaining suitable and healthy environment for our water critters. As currents begin to circulate it starts a series of essential events that are beneficial to all inhabitants.During the natural activity of living numerous types of waste begins to accumulate in the water column not only respiration from fish and plants but also from the activity of bacteria processing ammonia, organic nitrogen and other gasses.

Moving water is what transports excessive amounts of these waste – gasses to the surface releasing them into the atmosphere and picks up dissolved oxygen at the same time. Because moving water has more dissolved oxygen it is able to provide necessary nutrients to bacterial colonies giving nurturing expansion of the bacterial colony. Currents will clean the habitat by moving excessive organics to the filter.Currents will disturb the natural layering of water that occurs due to changing densities of water molecules (thermal gradient) increasing surface area for bacterial colonization and growth. One can think that water circulation stabilizes the quality of the water column.

In our aquariums the actual swimming area remains the same but by adding small amount of circulation and water movement can provide physical and engaging activity for our water critters. Maybe swimming against or through moving water our water critters could gain physical activity needed for proper growth and muscle development. Moving water then offers resistance to our water critters and may aide in their digestion, metabolism and other benefits of physical exercise.

Yet these important aspects of current and water movement are rarely identified or spoken. One reason that current and circulation is poorly represented is due to the dual notion we want to create realistic water motion that is both natural and adequate for our critters,

BUT, we must at the same time understand there is a real danger in creating the wrong type of water movement. The wrong type of water movement produces a very negative impact on aquaria by increasing levels of stress, denying access to necessary nutrition and corruption and degradation of the aquarium’s environment.

TermsCurrent: a body of water moving in a definite direction through a surrounding body of water in which there is less movement.Circulation: the movement of water to and fro or around in a closed system.

NATURAL CURRENT

The notion of convection has an impact on water movement in our aquariums and happens when water is heated in the presence of gravity, where gravity pulls down on all of the water molecules so that the bottom of the water column becomes denser with the weight of water molecules pushing down from the top of the water column.

Water at the boundary of the heater begins to heat-up. As the temperature climbs the water expands becoming less dense and the difference between the densities at the top of the aquarium and density of water at the bottom of the aquarium results in the gradual formation of circulating currents. The way this works ….. heated water surrounding the heating element begins to rise to the top of the aquarium displacing the colder denser water that was originally there forcing the colder denser water toward the bottom (heater) where it is heated and begins to rise resulting in the slow and expanding circulation currents.

All of my tanks are community. I try to set them up so that there is an area of moderate current and areas that are more still. Even fish native to violent rapids occasionally seek out boulders or ledges where they can rest. The idea of having a circulation strong enough to assist in gaseous exchange and distribution of nutrients seems perfectly logical to me.

If the aquarium has a filter rated for the tank volume, and provided the entire biological system is in balance, there will always be sufficient water movement to deal with the chemistry, temperature, and gas exchange.

The fact that one can have healthy aquaria with no filter at all is indicative that things work naturally, when there is a balance.

By "balance" I am meaning that the fish stocking is appropriate to the aquarium, in terms of numbers, species and sizes of fish. Obviously overloading the system will cause failure.

All natural waters are stratified with respect to temperature, and fish have evolved to deal with this.

The concern over water flow or current within the aquarium has to do with excesses either way, and this must be geared to the fish. I have had opportunity to observe this over the years in larger tanks where I can have stronger water flow at one end. I have always found that fish will for the most part remain within their preferred zones, both horizontally (substrate-level fish, mid-water fish, upper-water fish) and with respect to water flow. Except when feeding or if under stress, fish tend to remain where they feel most comfortable.

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian.[unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]

Hello Byron and fish monger:
These are very insightful statements. I didn’t know ‘a filter rated for the tank volume, and provided the entire biological system is in balance, there will always be sufficient water movement to deal with the chemistry, temperature, and gas exchange’.

What happens to water movement when the filter begins to clog or the biological system falls out of balance? I know you all don’t experience these types of problems due to being efficient managers but a sorry manager as me (assuming I am the only one) who’s entire biological system consistently falls out of balance with filtration capacity reduced needs to consider water circulation and making currents.
‘The concern over water flow or current within the aquarium has to do with excesses either way and this must be geared to the fish’ certainly sounds correct especially for efficient managers.
I guess I must muddle my way towards a current and circulation platform that works for my situation of unbalanced biological processes.

Hello Byron and fish monger:
These are very insightful statements. I didn’t know ‘a filter rated for the tank volume, and provided the entire biological system is in balance, there will always be sufficient water movement to deal with the chemistry, temperature, and gas exchange’.

What happens to water movement when the filter begins to clog or the biological system falls out of balance? I know you all don’t experience these types of problems due to being efficient managers but a sorry manager as me (assuming I am the only one) who’s entire biological system consistently falls out of balance with filtration capacity reduced needs to consider water circulation and making currents.

On the contrary, most of us likely do experience this, at least once. I recall a couple years ago sitting in front of my 115g 5-foot tank and it struck me that a few of the corys were respiring a bit fast, since they were just sitting still on a chunk of wood. I sat there trying to spot something for several minutes, until it finally dawned on me that the flow from the filter was not quite as strong as it normally was, and this I could detect from the sword plant's leaves right under the filter return. So, I disconnected the filter and cleaned it. It was dirty, indeed. Within minutes of reconnecting, the corys were respiring normally. This taught me that the canister on this tank needs more frequent cleaning than the canisters on my two other large tanks. And during the past 2 years, this has been proven accurate.

Acquiring a filter sufficient for the tank is fairly easy; one considers the type of fish to be housed, and if live plants are intended or not. In my case with small foredst fish and well planted tanks, I can select any canister rated for the tank volume. After that, I just have to remember to clean it regularly. I'm now at every 3 months. My smaller tanks, from 10g up to 33g, all have basic sponge filters which are rinsed at every weekly water change so nothing ever changes in these tanks with respect to flow.

The next step is not to overstock, and to ensure that all fish added to the tank are suited to the conditions of flow.

Quote:

‘The concern over water flow or current within the aquarium has to do with excesses either way and this must be geared to the fish’ certainly sounds correct especially for efficient managers.
I guess I must muddle my way towards a current and circulation platform that works for my situation of unbalanced biological processes.

Water changes are another important factor in all this, and doing them or not doing them does impact things. I do not want to get into that, but I mention it because it really is a major factor in the biology.

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian.[unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]

Since you brought it up I must concede that regular water changes not only makes sense now but appears to have a positive effect on the activity of the water critters.

I have lost the warm comfort of watching the critters calmly move through the water and now only see fields of bacteria consuming no-see-ums, considerations of water movement and guilt in counting the number of days until I must slave away toting water and cleaning filters.
Days of innocence pleasure have ended and digressed into hourly fears of excessive bio-load, redox and biochemical oxygen demand and carbon dioxide levels. The list never ends so I must remember not to feed the critters today; its time to tote more water can’t let the nitrates get out of hand.

I feel your pain, Pop. It is similar to having a back yard pool. By the time you finish maintenance, you've had your fill of it. There is a real sense of satisfaction that comes with the completion of the toting though. I just wish I had more time to enjoy my tanks. These days, it seems all of my aquarium time is spent on chores rather than the joy of observing.